Rat and bat brains have a built-in buddy-tracker

The journal Science has just published two interesting pieces of research that seem to confirm something about the brain. Neurons in the brain’s hippocampus do a dual shift, not only marking physical locations around us but also placing both friends and foe within that internal map, like our own “internal GPS”. We’ve known how mammals map their environment for some time, but the fact that other creatures are considered in this equation is news to scientists.

Researchers independently observed this trend in both rats and bats in two separate studies, and it seems highly likely that this phenomenon extends to critters that don’t rhyme with “cat” – including humans.

“Our findings show that the brain has a general mapping system that plots the locations of other people, objects and landmarks, in addition to knowing where oneself is located,” Dr Shigeyoshi Fujisawa, research group lead at the RIKEN Brain Science Institute, which conducted the rat study, tells me via email. “This is similar to the GPS system in your car that shows your car, terrain landmarks, store locations and traffic information.

“For rats, this general mapping system can be used for both social communication and predator recognition. We hypothesise that this system is commonly used in mammals, including humans.”

Here’s how the two sets of researchers reached their similar conclusions. With Fujisawa’s research, rats were placed in a simple T-shaped maze across a pair of studies, where they would be rewarded for either following a buddy rat or by going in the opposite direction. While their rodent brains were taking it all in, the researchers were examining the brain activity and found that hippocampal neurons lit up for environmental locations, but some showed a preference for the location of the buddy rat even when the goal was to ignore it and go the other way.

“These cells are not confused,” says Fujisawa. “We can reconstruct the paths of the pair of rats and reliably decode the location of the self or the other from the activity of these joint place cells.”

The bat-based study, conducted by the Weizmann Institute of Science in Israel, was subtly different but provided similar results. One bat would watch another fly to a hanging ball, and if it followed it would receive a treat. While this was happening, the researchers were looking at more than 350 bat-brain neurons, watching them flash into life when observing the bat-buddy. Crucially, when the researchers replaced the bat-buddy with an inanimate object providing the demo run, they noticed a marked difference in hippocampal activity: most interestingly, neurons demonstrated much higher levels of “spatial resolution” when the bats observed a living, breathing animal make the journey first.

“The basic take-home message is that in addition to mapping one’s own location, the hippocampus contains a cognitive mapping system that encodes the locations of other individuals,” Dr Fujisawa explains. “While we knew how self-position is mapped in the hippocampus, how others’ positions are mapped is a new discovery. Even rats are smart enough to have these kinds of high-level cognitive functions.”

Does that mean if the location-mapping part of the brain was damaged, then animals would struggle to track other creatures? “We think so,” Fujisawa replies. “In our Science paper, we showed that when the hippocampus is temporarily inactivated with a drug injection, performance on the observation task was significantly reduced.”

The research certainly raises a lot of questions, and for Dr Fujisawa there’s plenty more to be gleaned by digging into the neuronal circuitry that forms the mapping system. “For example, how does the hippocampus integrate ‘self’ and ‘other’ locations that are pre-processed in different brain regions?” he asks.

Hopefully, we’ll have more answers soon.